I bought a few PFC8574 and 4x4 keypads for a small project. I'm unclear on the correct wiring of the keypad to the PFC8574.

On the Arduino Playground's site, there are pull-up resistors for each column, but on a few other sites (like this one that I can't read, but I understand a schematic and there's a third example too, but I don't have the reputation to post it), the wiring does straight into the IC.

Does it depend on the library that's being used? Or what am I missing?


1 Answer 1


Ok look at this image: enter image description here

I'm not sure how your keypad is layed out but if you use a probe pin to test your connections via a multimeter, you can mark which ones correspond to the image.

I am ASSUMING you are going to use the code from arduino playground.

This is the format:

Pins of keypad (IN THE IMAGE) - Pins of PFC8547

Here are the pin connections:

1 - nothing

2 - 9

3 - 4

4 - 6

5 - 7

6 - 10

7 - 11

8 - 5

Also include the pull-up resistors. Your ABCD keys will be ignored

(This is like wiring a bomb...)

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